FR2911392A1 - Cryogenic argon producing unit for air separation apparatus, has unit for connecting head of argon mixture columns with denitrogenation column, and other unit for connecting tank of denitrogenation column with mixture columns - Google Patents

Abstract

The unit has an argon mixture column formed by primary and secondary argon mixture columns (K10-1, K10-2), and a denitrogenation column (K11), where a head of the primary argon mixture column is connected to a base of the secondary argon mixture column. A connection unit connects a head of the argon mixture columns with the denitrogenation column. Another connection unit connects a base of the denitrogenation column with the argon mixture columns. An independent claim is also included for a method for producing cryogenic argon by cryogenic distillation in an air separation apparatus.

Description

The present invention relates to a method and apparatus for producing

  of argon by cryogenic distillation. The scope of the present invention is delimited for air separation units equipped with a cryogenic argon production, i.e. an impure argon column (which allows separation of argon and oxygen) and a pure argon column (also called denitrogenation column which allows the elimination of nitrogen and thus obtain pure argon). The process of air distillation will not be presented in detail, it is considered to be a principle sufficiently explained in the literature.

  In a nutshell, this process is used to produce oxygen, nitrogen and argon (more rarely krypton and xenon) by compressing and then cooling (liquefying) and distilling ambient air. In a conventional system, the air is compressed and then separated using high and low pressure columns (which are more and more often "superimposed" and thermally communicating by an oxygen / nitrogen exchanger called vaporizer-condenser). In the high pressure column, the nitrogen is separated from the air by creating oxygen-rich liquid at the bottom of the column and liquid and nitrogen-rich vapor at the top of the column. These products are extracted and some are fed separately to the low pressure column. Because of differences in relative volatility between argon, nitrogen and oxygen, substantially pure nitrogen is formed at the top of the column, substantially pure oxygen is formed at the bottom of the column and gas rich in argon in the middle of the column. The central fraction, rich in argon, often called crude argon, is withdrawn from the low pressure column and feeds an auxiliary column (argon column) in order to ultimately produce argon. The raw argon is rectified into a rich oxygen reflux (which is subsequently sent to the low pressure column) and a very rich argon flow (often called argon mixture) which contains practically no oxygen (the content oxygen in the argon mixture is typically less than 3 ppm oxygen). This argon mixture is sent to a denitrogenation column to eliminate nitrogen by reboiling. At the bottom of the denitrogenation column pure argon is withdrawn in liquid form and is sent to a liquid Argon storage.

  The argon mixture column can be in two parts to reduce the size of the cold box. Below is an example of normal operation of the argon part. A maximum of argon is withdrawn at the top of the argon mixture column, which is in two parts. The nitrogen is then removed in the denitrogenation column. When the Argon storage is full, one can: • either stop the denitrogenation column, and also the unclean argon column, which takes time and has an impact on the low pressure column. In addition, the oxygen extraction yield is affected. The argon entering the cold box comes out partially with the liquid oxygen withdrawn at the bottom of the low pressure column and in the waste; • continue to extract argon, and purge it. This liquid purge is a loss of liquid, the argon entering the cold box spring essentially in purge form, the rest spring with the liquid oxygen withdrawn at the bottom of the low pressure column and in the waste. According to one aspect of the invention, there is provided a unit for producing argon by cryogenic distillation adapted to be connected to a double air separation column comprising a mixture column constituted by a mixture column (or a first and a second column of mixture) and a denitrogenation column, means for connecting the head of the mixture column or the head of the second column to the denitrogenation column and means for connecting the vessel of the denitrogenation column to the column of mixture or one of the first and second columns of mixture or double column.

  Optionally the mixture column is constituted by a first and a second column, the head of the first column being connected to the vessel of the second column. According to another aspect of the invention, there is provided an apparatus for separating air by cryogenic distillation comprising a double air separation column constituted by a high pressure column and a low pressure column connected thermally to each other, a unit of argon production as described above, means for supplying compressed and purified gaseous air to the high pressure column, means for supplying oxygen and nitrogen enriched fluids from the high pressure column to the low pressure column . According to another aspect of the invention, there is provided a method for producing argon by cryogenic distillation in a cryogenic distillation apparatus comprising a double air separation column constituted by a high pressure column and a low pressure column connected thermally. between them and an argon production unit comprising a mixture column constituted by a mixture column (or a first and a second mixture column) and a denitrogenation column, in which according to a first mode of operation, one sends the air at the high pressure column where it separates, nitrogen and oxygen enriched flow rates are sent from the high pressure column to the low pressure column, a flow enriched in argon from the low pressure column is withdrawn and sends to the mixture column (the first column of mixture), a rich argon flow is withdrawn from the mixture column (from the second column of mixture) and o It is sent to the denitrogenation column and according to a second mode of operation, the vessel liquid is sent from the denitrogenation column to the mixture column (to the second mixture column) and / or to the low pressure column.

  According to the second mode of operation it is possible to send tank liquid from the denitrogenation column to an intermediate level of the mixture column, (to the second mixture column) and according to the second mode of operation or a third mode of operation. can send liquid from an intermediate point of the mixture column (from the vessel of the second column of mixture) to the low pressure column. The second mode of operation may correspond to the start of the denitrogenation column. The second mode of operation may correspond to a period when no argon product is produced in the tank of the denitrogenation column.

  The invention will now be described in more detail with reference to the figures which show schematic drawings of air separation methods according to the invention. In FIG. 1, compressed air 1 is sent to the high pressure column K1 of a double column comprising high and low pressure columns K1, K2 superimposed and thermally communicating by an oxygen / nitrogen exchanger R1 called vaporizer-condenser. In the high pressure column, the nitrogen is separated from the air by creating oxygen-rich liquid at the bottom of the column and liquid and nitrogen-rich vapor at the top of the column. These products are extracted and some are fed separately to the low pressure column K2. Substantially pure nitrogen is formed at the top of the low pressure column K2, substantially pure oxygen is formed at the bottom of column K2 and argon rich gas in the middle of column K2. The central fraction 9, rich in argon, often called crude argon, is withdrawn from the low pressure column K2 and feeds a first column of K10-1 mixture in order to ultimately produce argon. The first K10-1 mixture column does not include a head condenser or a bottom reboiler. The crude argon is rectified into a rich oxygen reflux 11 (which is subsequently sent to the low pressure column K2) and an argon enriched gas 13.

  The argon-enriched gas is sent to the bottom of a second column of K10-2 mixture comprising a head condenser R2. There it separates into a very rich stream of argon 21 (often called argon mixture) which contains practically no more oxygen (the oxygen content in the argon mixture is conventionally less than 3 ppmO2). This argon mixture is sent to a denitrogenation column K11 in liquid or gaseous form in order to eliminate the nitrogen by reboiling. At the bottom of the denitrogenation column K11, pure argon 23 is withdrawn in liquid form and is sent to a liquid argon storage (not shown). The argon mixture column may be constituted by two columns, as illustrated here to reduce the size of the cold box, or may be constituted by a single column. When the argon storage is full, liquid argon 23 is produced at the bottom of the denitrogenation column K11 in the tank of the second mixture column K10-2 (gravity, but a pump could be used).

  This argon recycle returns to the low pressure column K2 via the lift pump P10 by opening the valve V1. The flow of argon 21 which enters the column K11 is approximately equal to the flow rate 19 which returns to the low pressure column K2. The liquid argon 19 arrives at the top of the low pressure column K2 (at the level of the rise of poor liquid, at the bottom of the minaret); by flash, the argon is extracted in gaseous form into the residual nitrogen 6. During a start of the argon part, comprising the two mixture columns and the denitrogenation column, the air is first vented. nitrogen in order to prime the mixture condenser. According to a method practiced, the vaporizer R2 is filled with rich liquid 7 at the top of the K10-2 mixture column, the mixture columns are first started (at almost total reflux so as to concentrate the argon in these columns as much as possible). ). Then the denitrogenation column K11 is started when the oxygen purities at the top of the mixture column are reached. The setting of the denitrogenation column K11 requires a few hours even by purging the liquid 23 several times at the bottom of the column to accelerate the setting of the liquid argon content. One application of the invention consists in sending the argon mixture to the denitrogenation column although the oxygen contents are not yet correct. The argon 23 withdrawn at the bottom of the denitrogenation column is then returned to column K10-2 through the open valve V3. The short circuit liquid argon circuit 19 at the outlet of the pump P10 remains closed by means of the valve V1 and the liquid 15 is sent entirely to the top of the first column of mixture K10-1. This keeps the argon (the molecules stay in the mixture column as if the mixture column was working in total reflux), in order to reach the grade specifications as fast as possible. By not purging liquid, we do not lose frigories.

  This allows the two columns (mixture column and denitration column) to be put into operation simultaneously. The oxygen content at the top of the mixing column and the oxygen content at the bottom of the denitrogenation column go down almost simultaneously, to reach the specification (3 ppm).

  The application of the invention makes it possible to gain valuable start-up hours of the argon part. Production is increased. For the case where the column of mixture is constituted by a single column K10, the apparatus is represented by FIG.

  Compressed air 1 is sent to the high pressure column K1 of a double column comprising high and low pressure columns K1, K2 superimposed and thermally communicating by an oxygen / nitrogen exchanger R1 called vaporizer-condenser. In the high pressure column, the nitrogen is separated from the air by creating oxygen-rich liquid at the bottom of the column and liquid and nitrogen-rich vapor at the top of the column. These products are extracted and some are fed separately to the low pressure column K2. Substantially pure nitrogen is formed at the top of the low pressure column K2, substantially pure oxygen is formed at the bottom of column K2 and argon rich gas in the middle of column K2. The central fraction 9, rich in argon, often called crude argon, is withdrawn from the low pressure column K2 and feeds the K10 mixture column in order to ultimately produce argon. The K10-mixture column does not include a R2 head condenser but no tank reboiler. The crude argon is rectified into an oxygen-rich reflux 11 (which is subsequently sent to the low-pressure column K2) and to a gas rich in argon, which contains practically no oxygen (the oxygen content in the argon mixture is conventionally less than 3 ppmO2). This argon mixture 21 is sent to a denitrogenation column K11 in liquid or gaseous form in order to eliminate the nitrogen by reboiling. At the bottom of the denitrogenation column K11, pure argon 23 is withdrawn in liquid form and is sent to a liquid argon storage (not shown). When the argon storage is full, liquid argon 23 is produced at the bottom of the denitrogenation column K11 at an intermediate level of the mixture column K10 (gravity, but a pump could be used). This argon recycle returns to the low pressure column K2 by withdrawing a liquid 19 at an intermediate level via the lift pump P10 by opening the valve V1. The flow of argon 21 which enters the column K11 is approximately equal to the flow rate 19 which returns to the low pressure column K2.

  The liquid argon 19 arrives at the top of the low pressure column K2 (at the level of the rise of poor liquid, at the bottom of the minaret); by flash, the argon is extracted in gaseous form in the residual nitrogen 6.

  When starting the argon portion, comprising the two mixture columns and the denitrogenation column, it is first put in the air nitrogen to be able to prime the mixture condenser. According to a method practiced, the vaporizer R2 is filled with rich liquid 7 at the top of the K10-2 mixture column, the mixture columns are first started (at almost total reflux so as to concentrate the argon in these columns as much as possible). ). Then the denitrogenation column K11 is started when the oxygen purities at the top of the mixture column are reached. The setting of the denitrogenation column K11 requires a few hours even by purging the liquid 23 several times at the bottom of the column to accelerate the setting of the liquid argon content. One application of the invention consists in sending the argon mixture to the denitrogenation column although the oxygen contents are not yet correct.

  The argon 23 withdrawn at the bottom of the denitrogenation column is then returned to column K10 through the open valve V3. The short circuit liquid argon circuit 19 at the outlet of the pump P10 remains closed by means of the valve V1 and the liquid 15 remains in the mixture column K10. This keeps the argon (the molecules stay in the mixture column as if the mixture column was working in total reflux), in order to reach the grade specifications as fast as possible. By not purging liquid, we do not lose frigories. This allows the two columns (mixture column and denitration column) to be put into operation simultaneously. The oxygen content at the top of the mixing column and the oxygen content at the bottom of the denitrogenation column go down almost simultaneously, to reach the specification (3 ppm). In the cases of Figure 1 and 2, the process can be simplified by sending the liquid argon directly to the low pressure column K2 without passing through a column of mixture.

Claims (7)

  A unit for producing argon by cryogenic distillation adapted to be connected to a double air separation column comprising a mixture column constituted by a mixture column (K10) (or a first and a second mixture column (K10 -1, K10-2) and a denitrogenation column (K11), means for connecting the head of the mixture column (or the head of the second mixture column) to the denitrogenation column and means for connecting the vessel from the denitrogenation column to the mixture column (or one of the first and second mixture columns) and / or to the double column.   2. Unit according to claim 1 wherein the mixture column is constituted by a first and a second column (K10-1, K10-2), the head of the first column being connected to the vessel of the second column.   3. Cryogenic distillation air separation apparatus comprising a double air separation column constituted by a high pressure column and a low pressure column (K1, K2) thermally connected to each other, an argon production unit according to the invention. One of the preceding claims means for supplying compressed and purified gaseous air to the high pressure column, means for supplying oxygen and nitrogen enriched fluids from the high pressure column to the low pressure column.   4. Process for the production of argon by cryogenic distillation in a cryogenic distillation apparatus comprising a double air separation column constituted by a high pressure column and a low pressure column (K1, K2) thermally connected to one another and argon production comprising a mixture column constituted by a mixture column (K10) (or a first and a second mixture column K10-1, K10-2) and a denitrogenation column (K11), wherein according to a first mode of operation, air is sent to the high pressure column where it separates, sends nitrogen and oxygen enriched flow rates of the high pressure column to the low pressure column, withdrawn argon enriched flow of the column low pressure and sent to the mixture column (the first column of mixture), a rich argon flow is withdrawn from the mixture column (from the second column of mixture K10-2), it is sent to the denitrogenation column and withdrawn an argon flow in the tank of the denitrogenation column as product and according to a second operating mode is sent liquid tank from the denitrogenation column to the mixture column, (in the second column of mixture) and / or the low pressure column.   5. The method according to claim 4, wherein according to the second mode of operation, vessel liquor is sent from the denitrogenation column to an intermediate level of the mixture column K10 (at the second mixture column K10-2) and according to the method. second mode of operation or a third mode of operation is sent liquid from an intermediate point of the mixture column K10 (of the tank of the second column of mixture K10-2) to the low pressure column.   6. The method of claim 4 or 5 wherein the second mode of operation corresponds to the start of the denitrogenation column.   7. The method of claim 4 or 5 wherein the second mode of operation corresponds to a period when no longer produces argon product in the tank of the denitrogenation column.